Microelectronic packages and methods therefor

ABSTRACT

A microelectronic package includes a microelectronic element having faces and contacts and a flexible substrate spaced from and overlying a first face of the microelectronic element. The package also includes a plurality of conductive posts extending from the flexible substrate and projecting away from the first face of the microelectronic element, wherein at least some of the conductive posts are electrically interconnected with the microelectronic element, and a plurality of support elements supporting the flexible substrate over the microelectronic element. The conductive posts are offset from the support elements to facilitate flexure of the substrate and movement of the posts relative to the microelectronic element.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S.Provisional Patent Application No. 60/533,210 filed Dec. 30, 2003,entitled “Microelectronic Packages and Methods Therefor,” the disclosureof which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to microelectronic packages and to methodsof making and testing microelectronic packages.

Microelectronic devices such as semiconductor chips typically requiremany input and output connections to other electronic components. Theinput and output contacts of a semiconductor chip or other comparabledevice are generally disposed in grid-like patterns that substantiallycover a surface of the device (commonly referred to as an “area array”)or in elongated rows which may extend parallel to and adjacent each edgeof the device's front surface, or in the center of the front surface.Typically, devices such as chips must be physically mounted on asubstrate such as a printed circuit board, and the contacts of thedevice must be electrically connected to electrically conductivefeatures of the circuit board.

Semiconductor chips are commonly provided in packages that facilitatehandling of the chip during manufacture and during mounting of the chipon an external substrate such as a circuit board or other circuit panel.For example, many semiconductor chips are provided in packages suitablefor surface mounting. Numerous packages of this general type have beenproposed for various applications. Most commonly, such packages includea dielectric element, commonly referred to as a “chip carrier” withterminals formed as plated or etched metallic structures on thedielectric. These terminals typically are connected to the contacts ofthe chip itself by features such as thin traces extending along the chipcarrier itself and by fine leads or wires extending between the contactsof the chip and the terminals or traces. In a surface mountingoperation, the package is placed onto a circuit board so that eachterminal on the package is aligned with a corresponding contact pad onthe circuit board. Solder or other bonding material is provided betweenthe terminals and the contact pads. The package can be permanentlybonded in place by heating the assembly so as to melt or “reflow” thesolder or otherwise activate the bonding material.

Many packages include solder masses in the form of solder balls,typically about 0.1 mm and about 0.8 mm (5 and 30 mils) in diameter,attached to the terminals of the package. A package having an array ofsolder balls projecting from its bottom surface is commonly referred toas a ball grid array or “BGA” package. Other packages, referred to asland grid array or “LGA” packages are secured to the substrate by thinlayers or lands formed from solder. Packages of this type can be quitecompact. Certain packages, commonly referred to as “chip scalepackages,” occupy an area of the circuit board equal to, or onlyslightly larger than, the area of the device incorporated in thepackage. This is advantageous in that it reduces the overall size of theassembly and permits the use of short interconnections between variousdevices on the substrate, which in turn limits signal propagation timebetween devices and thus facilitates operation of the assembly at highspeeds.

Assemblies including packages can suffer from stresses imposed bydifferential thermal expansion and contraction of the device and thesubstrate. During operation, as well as during manufacture, asemiconductor chip tends to expand and contract by an amount differentfrom the amount of expansion and contraction of a circuit board. Wherethe terminals of the package are fixed relative to the chip or otherdevice, such as by using solder, these effects tend to cause theterminals to move relative to the contact pads on the circuit board.This can impose stresses in the solder that connects the terminals tothe contact pads on the circuit board. As disclosed in certain preferredembodiments of U.S. Pat. Nos. 5,679,977; 5,148,266; 5,148,265;5,455,390; and 5,518,964, the disclosures of which are incorporated byreference herein, semiconductor chip packages can have terminals thatare movable with respect to the chip or other device incorporated in thepackage. Such movement can compensate to an appreciable degree fordifferential expansion and contraction.

Testing of packaged devices poses another formidable problem. In somemanufacturing processes, it is necessary to make temporary connectionsbetween the terminals of the packaged device and a test fixture, andoperate the device through these connections to assure that the deviceis fully functional. Ordinarily, these temporary connections must bemade without bonding the terminals of the package to the test fixture.It is important to assure that all of the terminals are reliablyconnected to the conductive elements of the test fixture. However, it isdifficult to make connections by pressing the package against a simpletest fixture such as an ordinary circuit board having planar contactpads. If the terminals of the package are not coplanar, or if theconductive elements of the test fixture are not coplanar, some of theterminals will not contact their respective contact pads on the testfixture. For example, in a BGA package, differences in the diameter ofthe solder balls attached to the terminals, and non-planarity of thechip carrier, may cause some of the solder balls to lie at differentheights.

These problems can be alleviated through the use of speciallyconstructed test fixtures having features arranged to compensate fornon-planarity. However, such features add to the cost of the testfixture and, in some cases, introduce some unreliability into the testfixture itself. This is particularly undesirable because the testfixture, and the engagement of the device with the test fixture, shouldbe more reliable than the packaged devices themselves in order toprovide a meaningful test. Moreover, devices intended for high-frequencyoperation typically must be tested by applying high frequency signals.This requirement imposes constraints on the electrical characteristicsof the signal paths in the test fixture, which further complicatesconstruction of the test fixture.

Additionally, when testing packaged devices having solder ballsconnected with terminals, solder tends to accumulate on those parts ofthe test fixture that engage the solder balls. This accumulation ofsolder residue can shorten the life of the test fixture and impair itsreliability.

A variety of solutions have been put forth to deal with theaforementioned problems. Certain packages disclosed in theaforementioned patents have terminals that can move with respect to themicroelectronic device. Such movement can compensate to some degree fornon-planarity of the terminals during testing.

U.S. Pat. Nos. 5,196,726 and 5,214,308, both issued to Nishiguchi etal., disclose a BGA-type approach in which bump leads on the face of thechip are received in cup-like sockets on the substrate and bondedtherein by a low-melting point material. U.S. Pat. No. 4,975,079 issuedto Beaman et al. discloses a test socket for chips in which dome-shapedcontacts on the test substrate are disposed within conical guides. Thechip is forced against the substrate so that the solder balls enter theconical guides and engage the dome-shaped pins on the substrate.Sufficient force is applied so that the dome-shaped pins actually deformthe solder balls of the chip.

A further example of a BGA socket may be found in commonly assigned U.S.Pat. No. 5,802,699, issued Sep. 8, 1998, the disclosure of which ishereby incorporated by reference herein. The '699 patent discloses asheet-like connector having a plurality of holes. Each hole is providedwith at least one resilient laminar contact extending inwardly over ahole. The bump leads of a BGA device are advanced into the holes so thatthe bump leads are engaged with the contacts. The assembly can betested, and if found acceptable, the bump leads can be permanentlybonded to the contacts.

Commonly assigned U.S. Pat. No. 6,202,297, issued Mar. 20, 2001, thedisclosure of which is hereby incorporated by reference herein,discloses a connector for microelectronic devices having bump leads andmethods for fabricating and using the connector. In one embodiment ofthe '297 patent, a dielectric substrate has a plurality of postsextending upwardly from a front surface. The posts may be arranged in anarray of post groups, with each post group defining a gap therebetween.A generally laminar contact extends from the top of each post. In orderto test a device, the bump leads of the device are each inserted withina respective gap thereby engaging the contacts which wipe against thebump lead as it continues to be inserted. Typically, distal portions ofthe contacts deflect downwardly toward the substrate and outwardly awayfrom the center of the gap as the bump lead is inserted into a gap.

Commonly assigned U.S. Pat. No. 6,177,636, the disclosure of which ishereby incorporated by reference herein, discloses a method andapparatus for providing interconnections between a microelectronicdevice and a supporting substrate. In one preferred embodiment of the'636 patent, a method of fabricating an interconnection component for amicroelectronic device includes providing a flexible chip carrier havingfirst and second surfaces and coupling a conductive sheet to the firstsurface of the chip carrier. The conductive sheet is then selectivelyetched to produce a plurality of substantially rigid posts. A compliantlayer is provided on the second surface of the support structure and amicroelectronic device such as a semiconductor chip is engaged with thecompliant layer so that the compliant layer lies between themicroelectronic device and the chip carrier, and leaving the postsprojecting from the exposed surface of the chip carrier. The posts areelectrically connected to the microelectronic device. The posts formprojecting package terminals that can be engaged in a socket orsolder-bonded to features of a substrate as, for example, a circuitpanel. Because the posts are movable with respect to the microelectronicdevice, such a package substantially accommodates thermal coefficient ofexpansion mismatches between the device and a supporting substrate whenthe device is in use. Moreover, the tips of the posts can be coplanar ornearly coplanar.

Despite all of the above-described advances in the art, still furtherimprovements in making and testing microelectronic packages would bedesirable.

SUMMARY OF THE INVENTION

One aspect of the invention provides a microelectronic packagecomprising which includes a microelectronic element such as asemiconductor chip and a flexible substrate spaced from and overlying afirst face of the microelectronic element. The package according to thisaspect of the invention desirably includes a plurality of conductiveposts extending from the flexible substrate and projecting away from themicroelectronic element, at least some of the conductive posts beingelectrically interconnected with said microelectronic element. Mostpreferably, the package according to this aspect of the inventionincludes a plurality of support elements disposed between themicroelectronic element and said substrate and supporting said flexiblesubstrate over the microelectronic element. Desirably, at least some ofthe conductive posts are offset in horizontal directions parallel to theplane of the flexible substrate from the support elements. For example,the support elements may be disposed in an array with zones of theflexible substrate disposed between adjacent support elements, and theposts may be disposed near the centers of such zones.

The offset between the posts and the support elements allows the posts,and particularly the bases of the posts adjacent the substrate, to moverelative to the microelectronic element. Most preferably, thearrangement allows each post to move independently of the other posts.The movement of the posts allows the tips of the plural posts tosimultaneously engage contact pads on a circuit board despiteirregularities in the circuit board or the package, such as warpage ofthe circuit board. This facilitates testing of the package using asimple test board which may have substantially planar contacts, andavoids the need for specialized, expensive test sockets.

Most preferably, the flexible substrate overlies the front orcontact-bearing face of the microelectronic element. At least some ofthe support elements desirably are electrically conductive elements suchas solder balls. The conductive support elements may electricallyinterconnect at least some of the contacts of the microelectronicelement with at least some of the conductive posts. In preferred forms,this arrangement can prove low-impedance conductive paths between theposts and the microelectronic element, suitable for high-frequencysignal transmission. Most desirably, at least some of the posts areconnected to at least some of the contacts on the microelectronicelement by conductive support elements immediately adjacent to thoseposts. Preferably, conductive traces provided on the flexible substrateelectrically interconnect at least some of the conductive posts with atleast some of the conductive support elements. These traces may be veryshort; the length of each trace desirably is equal to the offsetdistance between a single post and a single support element.

A further aspect of the present invention provides a microelectronicassembly which desirably includes a package as discussed above and acircuit panel having contact pads. Tips of the posts remote from theflexible substrate confront the contact pads and are electricallyconnected thereto, most preferably by electrically conductive bondingmaterial such as solder. As further discussed below, the assembly can becompact and highly reliable.

A further aspect of the invention provides a microelectronic packagewhich includes a microelectronic element and a flexible substrate spacedfrom and overlying said microelectronic element. The flexible substrateis supported above said front face of said microelectronic element sothat said substrate is at least partially unconstrained in flexure. Forexample, the flexible substrate may be supported by support elements asdescribed above, or by other means such as a continuous compliant layer.Here again, the package includes a plurality of conductive postsextending from the flexible substrate and projecting away from themicroelectronic element, the conductive posts being electricallyconnected to the microelectronic element. The conductive posts havebases facing toward the flexible substrate. The package according tothis embodiment of the invention desirably includes elements referred toherein as “focusing elements” disposed between the bases of at leastsome of the posts and the substrate and mechanically interconnecting thebases of the conductive posts with the substrate. The focusing elementsdesirably have smaller areas than the bases of the posts. As furtherdiscussed below, this arrangement facilitates flexing of the substrateand movement of the posts.

Yet another aspect of the invention provides methods of processingmicroelectronic packages. Method according to this aspect of theinvention desirably include the step of advancing a microelectronicpackage having a flexible substrate supported over a surface of amicroelectronic element and having electrically conductive postsprojecting from said substrate until tips of said posts engage contactpads on a test circuit panel and the substrate flexes so that at leastsome base portions of said posts adjacent said flexible substrate moverelative to the microelectronic element. In preferred methods accordingto this aspect of the present invention, movement of the bases of theposts contribute to movement of the tips, allowing the tips to engagecontact pads even where the contact pads themselves are not coplanarwith one another.

The method according to this aspect of the invention may include thefurther steps of maintaining the tips of the posts in contact with saidcontact pads and testing the package during the maintaining step, as bytransmitting signals to and from the package through the engaged contactpads and posts. The method may be practiced using a simple circuitpanel, with simple contact pads. The method may further includedisengaging the tips from the contact pads after testing, and may alsoinclude bonding the tips of the posts to electrically conductiveelements of a circuit panel after disengagement from the test circuitpanel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic sectional view of a package according to oneembodiment of the invention.

FIG. 2 is a fragmentary plan view of the package shown in FIG. 1.

FIG. 3 is a diagrammatic elevational view depicting the package of FIGS.1-2 in conjunction with a test circuit panel during one step of a methodaccording to one embodiment of the invention.

FIG. 4 is a view similar to FIG. 3 but depicting a later stage of themethod.

FIG. 5 is a diagrammatic, idealized perspective view depicting a portionof the package shown in FIGS. 1-4.

FIG. 6 is a fragmentary sectional view depicting a portion of anassembly including the package of FIGS. 1-5.

FIGS. 7-10 are fragmentary sectional views depicting packages accordingto additional embodiments of the invention.

FIG. 11 is a diagrammatic perspective view depicting a package accordingto a further embodiment of the invention.

FIG. 12 is a diagrammatic sectional view of the package shown in FIG.11.

FIGS. 13 and 14 are fragmentary plan views similar to FIG. 2 butdepicting packages according to further embodiments of the invention.

FIGS. 15 and 16 are diagrammatic sectional view depicting packagesaccording to still further embodiments of the invention.

FIG. 17 is a fragmentary plan view depicting a portion of a packageaccording to yet another embodiment of the invention.

FIG. 18 is a fragmentary sectional view taken along line 18-18 in FIG.17.

FIG. 19 is a diagrammatic elevational view depicting components usablein the embodiment of FIGS. 17 and 18.

FIG. 20 is a diagrammatic top plan view of a package in accordance withanother embodiment of the invention.

FIG. 21 is a fragmentary, diagrammatic sectional view taken along line21-21 in FIG. 20.

FIGS. 22A-22D show a method of making a microelectronic assembly, inaccordance with certain preferred embodiments of the present invention.

FIG. 23 shows a method of making a microelectronic assembly, inaccordance with further preferred embodiments of the present invention.

DETAILED DESCRIPTION

A microelectronic package 80, in accordance with one embodiment of thepresent invention, includes a microelectronic element, such as asemiconductor chip 82, having a front or contact bearing face 84 andelectrical contacts 83 exposed at face 84. A passivation layer 86 may beformed over the contact bearing face 84 with openings at contacts 83.

The microelectronic package 80 also includes conductive support elements88 such as solder balls in substantial alignment and electricallyinterconnected with contacts 83. As best seen in FIG. 2, contacts 83 andsupport elements 88 are disposed in an array which in this case is arectilinear grid, having equally spaced columns extending in a firsthorizontal direction x and equally spaced rows extending in a secondhorizontal direction y orthogonal to the first horizontal direction.Each contact 83 and support element 88 is disposed at an intersection ofa row and a column, so that each set of four support elements 88 atadjacent intersections, such as support elements 88 a, 88 b, 88 c and 88d, defines a generally rectangular, and preferably square, zone 89. Thedirections referred to in this disclosure are directions in the frame ofreference of the components themselves, rather than in the normalgravitational frame of reference. Horizontal directions are directionsparallel to the plane of the front surface 84 of the chip, whereasvertical directions are perpendicular to that plane.

The package also includes a flexible dielectric substrate 90, such as apolyimide or other polymeric sheet, including a top surface 92 and abottom surface 94 remote therefrom. Although the thickness of thedielectric substrate will vary with the application, the dielectricsubstrate most typically is about 10 μm-100 μm thick. The flexible sheet90 has conductive traces 96 thereon. In the particular embodimentillustrated in FIG. 1, the conductive traces are disposed on the bottomsurface 94 of the flexible sheet 90. However, in other embodiments, theconductive traces 96 may extend on the top surface 92 of the flexiblesheet 90; on both the top and bottom faces or within the interior offlexible substrate 90. Thus, as used in this disclosure, a statementthat a first feature is disposed “on” a second feature should not beunderstood as requiring that the first feature lie on a surface of thesecond feature. Conductive traces 96 may be formed from any electricallyconductive material, but most typically are formed from copper, copperalloys, gold or combinations of these materials. The thickness of thetraces will also vary with the application, but typically is about 5μm-25 μm. Traces 96 are arranged so that each trace has a support end100 and a post end 102 remote from the support end.

Electrically conductive posts or pillars 98 project from the top surface92 of flexible substrate 90. Each post 98 is connected to the post end102 of one of the traces 96. In the particular embodiment of FIGS. 1 and2, the posts 98 extend upwardly through the dielectric sheet 92, fromthe post ends of the traces. The dimensions of the posts can vary over asignificant range, but most typically the height h_(p) of each postabove the top surface 92 of the flexible sheet is about 50-300 μm. Eachpost has a base 74 adjacent the flexible sheet 90 and a tip 76 remotefrom the flexible sheet. In the particular embodiment illustrated, theposts are generally frustoconical, so that the base 74 and tip 76 ofeach post are substantially circular. The bases of the posts typicallyare about 100-600 μm in diameter, whereas the tips typically are about40-200 μm in diameter. The posts may be formed from any electricallyconductive material, but desirably are formed from metallic materialssuch as copper, copper alloys, gold and combinations thereof. Forexample, the posts may be formed principally from copper with a layer ofgold at the surfaces of the posts.

The dielectric sheet 92, traces 96 and posts 98 can be fabricated by aprocess such as that disclosed in co-pending, commonly assigned U.S.Provisional Patent Application Ser. No. 60/508,970, the disclosure ofwhich is incorporated by reference herein. As disclosed in greaterdetail in the '970 Application, a metallic plate is etched or otherwisetreated to form numerous metallic posts projecting from the plate. Adielectric layer is applied to this plate so that the posts projectthrough the dielectric layer. An inner or side of the dielectric layerfaces toward the metallic plate, whereas the outer side of thedielectric layer faces towards the tips of the posts. The dielectriclayer may be fabricated by coating a dielectric such as polyimide ontothe plate around the posts or, more typically, by forcibly engaging theposts with the dielectric sheet so that the posts penetrate through thesheet. Once the sheet is in place, the metallic plate is etched to formindividual traces on the inner side of the dielectric layer.Alternatively, conventional processes such as plating may form thetraces or etching, whereas the posts may be formed using the methodsdisclosed in commonly assigned U.S. Pat. No. 6,177,636, the disclosureof which is hereby incorporated by reference herein. In yet anotheralternative, the posts may be fabricated as individual elements andassembled to the flexible sheet in any suitable manner, which connectsthe posts to the traces.

As best appreciated with reference to FIG. 2, the support ends 100 ofthe leads are disposed in a regular grid pattern corresponding to thegrid pattern of the support elements, whereas the posts 98 are disposedin a similar grid pattern. However, the grid pattern of the posts isoffset in the first and second horizontal directions x and y from thegrid pattern of the support ends 100 and support elements 88, so thateach post 98 is offset in the −y and +x directions from the support end100 of the trace 96 connected to that post.

The support end 100 of each trace 96 overlies a support element 88 andis bonded to such support element, so that each post 98 is connected toone support element. In the embodiment illustrated, where the supportelements are solder balls, the bonds can be made by providing thesupport elements on the contacts 83 of the chip and positioning thesubstrate or flexible sheet 90, with the posts and traces already formedthereon, over the support elements and reflowing the solder balls byheating the assembly. In a variant of this process, the solder balls canbe provided on the support ends 100 of the traces. The process stepsused to connect the support ends of the traces can be essentially thesame used in flip-chip solder bonding of a chip to a circuit panel.

As mentioned above, the posts 98 are offset from the support elements 88in the x and y horizontal directions. Unless otherwise specified herein,the offset distance d_(o) (FIG. 2) between a post and a support elementcan be taken as the distance between the center of area of the base 74(FIG. 1) of the post and the center of area of the upper end 77 (FIG. 1)of the support element 88. In the embodiment shown, where both the baseof the post and the upper end of the support element have circularcross-sections, the centers of area lie at the geometric centers ofthese elements. Most preferably, the offset distance d_(o) is largeenough that there is a gap 99 (FIG. 2) between adjacent edges of thebase of the post and the top end of the support element. Stated anotherway, there is a portion of the dielectric sheet 90 in gap 99, which isnot in contact with either the top end 77 of the support element or thebase 74 of the post.

Each post lies near the center of one zone 89 defined by four adjacentsupport elements 88, so that these support elements are disposed aroundthe post. For example, support elements 88 a-88 d are disposed aroundpost 98 a. Each post is electrically connected by a trace and by one ofthese adjacent support elements to the microelectronic device 82. Theoffset distances from a particular post to all of the support elementsadjacent to that post may be equal or unequal to one another.

In the completed unit, the upper surface 92 of the substrate or flexiblesheet 92 forms an exposed surface of the package, whereas posts 98project from this exposed surface and provide terminals for connectionto external elements.

The conductive support elements 88 create electrically conductive pathsbetween the microelectronic element 82 and the flexible substrate 90 andtraces 96. The conductive support elements space the flexible substrate90 from the contact bearing face 84 of microelectronic element 82. Asfurther discussed below, this arrangement facilitates movement of theposts 98.

In a method of operation according to a further embodiment of theinvention, a microelectronic package 80 such as the package discussedabove with reference to FIGS. 1 and 2 is tested by juxtaposing theconductive posts 98 with contact pads 95 on a second microelectronicelement 97 such as a circuitized test board (FIG. 3). The conductiveposts 98A-98D are placed in substantial alignment with top surfaces ofthe respective contact pads 95A-95D. As is evident in the drawingfigure, the top surfaces 36A-36D of the respective contact pads 95A-95Dare disposed at different heights and do not lie in the same plane. Suchnon-planarity can arise from causes such as warpage of the circuit board97 itself and unequal thicknesses of contact pads 95. Also, although notshown in FIG. 3, the tips 76 of the posts may not be precisely coplanarwith one another, due to factors such as unequal heights of supportelements 88; non-planarity of the front surface 84 of themicroelectronic device; warpage of the dielectric substrate 90; andunequal heights of the posts themselves. Also, the package 80 may betilted slightly with respect to the circuit board. For these and otherreasons, the vertical distances Dv between the tips of the posts and thecontact pads may be unequal.

Referring to FIG. 4, the microelectronic package 80 is moved toward thetest board 97, by moving either the test board, the package or both. Thetips 76 of the conductive posts 98A-98D engage the contact pads 95 andmake electrical contact with the contact pads. The tips of the posts areable to move so as to compensate for the initial differences in verticalspacing Dv (FIG. 3), so that all of the tips can be brought into contactwith all of the contact pads simultaneously using only a moderatevertical force applied to urge the package and test board 97 together.In this process, at least some of the post tips are displaced in thevertical or z direction relative to other post tips.

A significant portion of this relative displacement arises from movementof the bases 74 of the posts relative to one another and relative tomicroelectronic element 80. Because the posts are attached to flexiblesubstrate 90 and are offset from the support elements 88, and becausethe support elements space the flexible substrate 90 from the frontsurface 84 of the microelectronic element, the flexible substrate candeform. Further, different portions of the substrate associated withdifferent posts can deform independently of one another. An idealizedrepresentation of the deformation of a single region 89 of substrate 90is shown in FIG. 5. The support elements 88 disposed at the corners ofthe region allow the central part of the region to bend downwardlytoward the microelectronic element 82, allowing the base of post 98 toalso move downward toward the microelectronic element. This deformationis idealized in FIG. 5 as a pure displacement of the post and the centerof the region in the vertical or z direction. In practice, thedeformation of the substrate may include bending and/or stretching ofthe substrate so that the motion of the base may include a tilting aboutan axis in the x-y or horizontal plane as well as some horizontaldisplacement of the base, and may also include other components ofmotion. For example, one portion of the region is reinforced by trace96, and will tend to be stiffer than the other portions of the region.Also, a particular post may be positioned off-center in its region 89,so that the post lies closer to one support element, or to a pair ofsupport elements, on one side of the post. For example, post 98 a (FIG.2) may be disposed closer to support elements 88 a and 88 b than tosupport elements 88 c and 88 d. The relatively small portion of thesubstrate between the post and support elements 88 a and 88 b will bestiffer in bending than the relatively large portion of the substratebetween the posts and support elements 88 c and 88 d. Suchnon-uniformities tend to promote non-uniform bending and hence tiltingmotion of the posts. Tilting of the posts tends to move the tips 76toward the microelectronic element. The support elements 88 at thecorners of the individual regions substantially isolate the variousregions from one another, so that the deformation of each region issubstantially independent of the deformation of other regions of thesubstrate 90. Depending on the configuration of the posts, the posts 98themselves may also flex or buckle to some degree, which providesadditional movement of tips 76 in the vertical or z direction.

The independent displacement of the posts relative to one another allowsall of the post tips 76 to contact all of the contact pads 95 on thetest substrate. For example, the flexible substrate 90 in the vicinityof conductive post 98C flexes substantially more than the flexiblesubstrate in the vicinity of conductive post 98B. In turn, the flexiblesubstrate 90 in the vicinity of conductive post 98B flexes substantiallymore than the flexible substrate in the vicinity of conductive post 98A.

Because all of the post tips 76 can be engaged reliably with all of thecontact pads 95, the package can be tested reliably by applying testsignals, power and ground potentials through the test circuit board 97and through the engaged posts and contact pads. Moreover, this reliableengagement is achieved with a simple test circuit board 97. For example,the contact pads 95 of the test circuit board are simple, planar pads.The test circuit board need not incorporate special features tocompensate for non-planarity or complex socket configurations. The testcircuit board can be made using the techniques commonly employed to formordinary circuit boards. This materially reduces the cost of the testcircuit board, and also facilitates construction of the test circuitboard with traces (not shown) in a simple layout compatible withhigh-frequency signals. Also, the test circuit board may incorporateelectronic elements such as capacitors in close proximity to the contactpads as required for certain high-frequency signal processing circuits.Here again, because the test circuit board need not incorporate specialfeatures to accommodate non-planarity, placement of such electronicelements is simplified. In some cases, it is desirable to make the testcircuit board as planar as practicable so as to reduce the non-planarityof the system and thus minimize the need for pin movement. For example,where the test circuit board is highly planar a ceramic circuit boardsuch as a polished alumina ceramic structure, only about 20 μm of pinmovement will suffice.

The internal features of package 80 are also compatible withhigh-frequency signals. The conductive support elements, traces andposts provide low-impedance signal paths between the tips of the postsand the contacts 83 of the microelectronic element. Because each post 98is connected to an immediately adjacent conductive support element 88,traces 96 are quite short. The low-impedance signal paths areparticularly useful in high-frequency operation, as, for example, wherethe microelectronic element must send or receive signals at a frequencyof 300 MHz or more.

After testing the microelectronic package 80 may be removed from thetest circuit board 97 and permanently interconnected with anothersubstrate such as a circuit panel 106 (FIG. 6) having contact pads 104,as by bonding the tips 76 of posts 98 to the contact pads of the circuitpanel using a conductive bonding material 99 such as a solder. Thesolder-bonding process may be performed using conventional equipmentcommonly used for surface-mounting microelectronic components. Thus, thesolder masses may be provided on the posts 98 or on the contact pads104, and may be reflowed after engaging the posts with the contact pads.During reflow, the surface tension of the solder tends to center theposts on the contact pads. Such self-centering action is particularlypronounced where the tips of the posts are smaller than the contactpads. Moreover, the solder 99 wets the sides of the posts to at leastsome extent, and thus forms a fillet encircling the tip of each post, aswell as a strong bond between the confronting surfaces of the posts andpads.

Moreover, the tips 76 of the posts 98 can move relative to themicroelectronic element 82 to at least some degree during service so asto relieve stresses arising from differential thermal expansion andcontraction. As discussed above in connection with the testing step, theindividual posts 98 can move relative to the microelectronic element andrelative to the other posts by flexure or other deformation of substrate90. Such movement can appreciably relieve stresses in the solder bondsbetween the posts and the contact pads which would otherwise occur upondifferential thermal expansion or contraction of the circuit board 106and microelectronic element 80. Moreover, the conductive supportelements or solder balls 88 can deform to further relieve stresses insolder masses 99. The assembly is highly resistant to thermal cyclingstresses, and hence highly reliable in service.

An underfill material (not shown) such as an epoxy or other polymericmaterial may be provided around the tips of the posts and around thecontact pads, so as to reinforce the solder bonds. Desirably, thisunderfill material only partially fills the gap between the package 80and the circuit board 106. In this arrangement, the underfill does notbond the flexible substrate 90 or the microelectronic device to thecircuit board. The underfill only reinforces the posts at their jointswith the contact pads. However, no reinforcement is required at thebases of the posts, inasmuch as the joint between the base of each postand the associated trace is extraordinarily resistant to fatiguefailure.

The assembly is also compact. Some or all of the posts 98 and contactpads 104 are disposed in the area occupied by the microelectronicelement 80, so that the area of circuit board 106 occupied by theassembly may be equal to, or only slightly larger than, the area of themicroelectronic element itself, i.e., the area of the front surface 84of the microelectronic element 80.

FIG. 7 shows a portion of a microelectronic package 1380 in accordancewith another embodiment of the present invention. This package includesa microelectronic element 1382, such as a semiconductor chip, havingcontacts 1383 on a face surface thereof. The package also includes aflexible substrate 1390 such as a flexible dielectric film having a topsurface 1392, a bottom surface 1394, conductive traces 1396 andconductive posts 1398 projecting from the top surface 1392. Theconductive posts 1398 are electrically interconnected with traces 1396at the bases of the posts. One or more of the conductive traces 1396 areelectrically interconnected with contacts 1383 by conductive elements1388. These features may be similar to the corresponding features of theembodiment discussed above with reference to FIGS. 1-6. In theembodiment shown in FIG. 7, each conductive support element 1388includes two conductive elements stacked one atop another so that afirst conductive element 1388A is positioned over a second conductiveelement 1388B. Conductive elements 1388A and 1388B are fused with oneanother to from an elongated conductive element 1388. In other preferredembodiments, three or more conductive elements may be stacked one atopanother between conductive trace 1396 and contact 1383. The stacking ofthe conductive elements enables the height of the flexible substrate1390 to be adjusted relative to the surface of the semiconductor chip1382. This provides additional clearance between the flexible substrate1390 and the chip surface 1384, which can accommodate additionaldisplacement of the post bases. Moreover, the elongated conductiveelements 1388 are more readily deformable, which can provide additionalmovability to the posts.

In the embodiment of FIG. 7, a compliant material 1327 is positionedbetween the flexible substrate 1390 and the microelectronic element1382. The compliant layer 1327 preferably does not substantiallyrestrict movement of the posts. The compliant material preventscontaminants from entering the package. Merely by way of example,compliant material 1327 may be a gel, foam or the like. Despite thepresence of the compliant material, conductive elements 1388 stillsupport the flexible substrate 1390 to a substantial degree.

Referring to FIG. 8, a package according to a further preferredembodiment of the present invention is similar to the packages discussedabove, except that each conductive support elements 1088 includes a core1089 covered by an outer conductive coating 1091. Core 1089 may be aconductive, high-melting material such as copper, whereas coating 1091may be a lower-melting material such as a solder. Alternatively, core1089 may be formed from a nonconductive material such as glass, ceramicor a polymer.

In a package according to yet another preferred embodiment of thepresent invention, the conductive support elements include elongatedconductive pillars 1188. These pillars may be formed integrally withtraces 1196 and posts 1198. The tips of pillars 1188 abut the contacts(not shown) of microelectronic element 1182, and may be bonded to thecontacts by a solder, eutectic bonding material, diffusion bond or othermetallurgical bond.

FIG. 10 shows a microelectronic package 1480 in accordance with yetanother preferred embodiment of the present invention. Themicroelectronic package 1480 includes a microelectronic element 1482such as a semiconductor chip having a front or contact-bearing surfacewith contacts 1483. The microelectronic element 1482 has a relativelyfine pitch so that the contacts 1483 and support elements 1488 arerelatively close to one another. In this arrangement, the offsetdistance D_(o) between the base 1474 of each post and the adjacentsupport elements 1488 is relatively small; a portion of the base mayoverlap with the adjacent support elements. Here again, flexiblesubstrate 1490 includes top surface 1492 and bottom surface 1494 remotetherefrom, and conductive traces 1496 are provided on the flexiblesubstrate. In this embodiment, the package also includes a focusingconductive element 1485 positioned between the base 1474 of eachconductive post 1498 and the top surface 1492 of flexible substrate1490. The focusing or second conductive element 1485 has a smaller areathan does the base of conductive post 1498. The focusing conductiveelements mechanically interconnect the bases of the posts with theflexible substrate and traces 1496, and also electrically interconnectthe posts and the traces. The relatively small area of the focusingelements helps to maintain the flexibility of the flexible substrate1490 and traces. Stated another way, the focusing conductive elements1485 facilitate movement of the conductive posts 1495 in a fine pitchenvironment. The focusing conductive elements can be formed integrallywith the posts and traces as, for example, by etching the bases of theposts after protecting the remainder of the posts using a suitable maskor plating. Focusing conductive elements can be employed to enhance themovability of conductive posts in structures where a flexible substrateis supported by elements other than support elements. For example,focusing conductive elements can be provided in structures of the typeshown in embodiments of the aforementioned U.S. Pat. No. 6,177,636 wherea flexible substrate is supported only by a compliant layer or bycompliant pads disposed beneath the posts.

As shown in FIGS. 11 and 12, a microelectronic package 1680 according toa further embodiment includes a microelectronic element 1682, such as asemiconductor chip, having contacts 1683 exposed at a front surfacethereof. In this embodiment, however, the contacts 1383 are not disposedin a uniform array but instead are disposed in rows 1604 disposedadjacent the edges 1602 of the chip. Each row thus extends in a rowdirection R in the horizontal plane of the chip front surface, such rowdirection being parallel to the edges of the chip. Here again, thepackage includes a flexible dielectric substrate 1690, having a topsurface 1692 and a bottom surface 1694. The flexible substrate 1690includes contact pads 1633 disposed on top surface 1692 and accessibleat bottom surface 1694 through holes in the substrate. Conductive traces1696 extend from the contact pads to posts 1698. Here again, theflexible substrate 1690 is assembled with the microelectronic element1682 using conductive elements 1688, such as solder balls. Here again,the conductive elements 1688 space and at least partially support theflexible substrate 1680 over the contact bearing face of themicroelectronic element 1682. In addition, the conductive elements 1688form an electrical interconnection between contacts 1684 ofmicroelectronic element 1682 and conductive pads 1633 of flexiblesubstrate 1690, and thus connect posts 1698 to contacts 1683. Themicroelectronic package 1680 optionally includes a compliant layer 1627,such as a curable elastomer, gel or the like disposed between the bottomsurface 1694 of flexible substrate 1690 and the font face ofmicroelectronic element 1682. In a further variant, the compliant layermay also comprise a porous compliant layer formed from a multiplicity ofpads defining channels between the pads. A curable elastomer optionallymay be injected in the channels between the compliant pads, as disclosedin commonly assigned U.S. Pat. No. 5,659,952, the disclosure of which ishereby incorporated by reference herein.

Here again, posts 1698 are offset from the support elements 1688 andcontacts 1683. In this case, the offset directions of the posts aretransverse to the row directions R. That is, each post is offset fromthe associated contact pad 1633, support element 1688 and contact pad1683 in a direction transverse to the row direction of the rowcontaining the associated contact pad 1683. The offset directions pointinwardly, toward the geometric center of the chip front surface, so thatthe posts are disposed inside the area bounded by the rows. Statedanother way, traces 1696 fan in from the contact pads 1633 to the posts1698.

Referring to FIG. 11, the flexible substrate 1690 has an opening 1635 soas to enhance the flexibility of the flexible substrate. In thisembodiment as well, the conductive posts have can move relative to thecontact bearing face of the microelectronic element 1682.

In a further, related embodiment shown in FIGS. 20 and 21, the chip 2202has contacts 2283 disposed in rows, each such row extending in a rowdirection R. In this embodiment as well, each row is disposed adjacentto an edge of the chip. Here again, conductive support elements 2288 areprovided on the contacts. In this embodiment, the conductive supportelements are in the form of studs rather than solder balls. Studs aresmall conductive elements applied in a process commonly referred to as“stud bumping”. For example, each stud may include a small mass of ametal such as gold or aluminum. The stud bumping process may beperformed using equipment similar to that employed in wire bonding. Thebonding tool typically carries a small ball of the metal, and bonds theball to the chip contact using heat, sonic vibrations, pressure or somecombination of these. In other stud bumping techniques, numerous studbumps are applied to numerous contacts simultaneously. The stud bumpingprocess can be performed on a wafer, prior to subdividing the wafer intoindividual chips.

In the embodiment of FIGS. 20 and 21, the posts 2298 are disposed on aflexible dielectric substrate 2290 carrying traces 2296. Posts 2298 aredisposed in rows which extend generally parallel to the rows of contactsand support elements. However, the posts associated with each row ofcontacts and support elements are offset from the support elements insuch row in two opposite directions transverse to the row direction.Thus, post 2298 a is offset from the row in one direction O₁ (to theright as seen in FIG. 20) whereas post 2298 b is offset in the oppositedirection O₂ (to the left as seen in FIG. 20). The opposite offsetssplit the posts 2298 associated with each row of contacts and supportelements into two rows, one such row of posts lying inboard of the rowof support elements 2283 and the other such row of posts lying outboardof the row of support elements. This arrangement increases the spacingbetween adjacent posts; such spacing, on average, will be about twicethe spacing between adjacent contacts on the chip. This is advantageousin that it allows for larger contact pads on the circuit board or othersubstrate to which the unit will be attached and also decreases theprecision required in placing the unit onto the circuit board. Moreover,placing the posts associated with each row of contacts and supportelements on opposite sides of the row of contacts and support elementsminimizes shear loads in horizontal directions applied to the conductivesupport elements when the posts are engaged with contacts pads on asubstrate. Forces applied to the tips of the posts tending to bend thesubstrate 2290 and traces 2296 may also place the substrate in tension,and may apply horizontally directed force components to the supportelements. However, the horizontally directed components applied by postson opposite sides of the row of support elements (such as by posts 2296a and 2296 b) tend to balance one another. Stated another way, eachsupport element 2283 lies between posts.

In the particular embodiment of FIGS. 20 and 21, the flexible substrate2290 extends outwardly beyond the edges of chip 2202, and those postsdisposed outboard of the contacts (such as post 2296 a) are disposed inwhole or in part beyond the edges of the chip. To provide additionalsupport for these posts, a support element (not shown) may encircle thechip. Alternatively or additionally, an encapsulant (not shown)optionally may be provided around the edges of the chip, and optionallybetween the chip and substrate 2290.

Numerous further variations and combinations of the features discussedabove can be used. For example, where the contacts on a chip aredisposed in an array, such array need not be a rectilinear, regulararray as shown in FIG. 2. For example, as shown in FIG. 13, the contactsand support elements 1788 may be disposed in an irregular pattern or ina hexagonal or triangular array. In the particular pattern of FIG. 13,post 1798 a lies in a region 1789 bounded by three support elements 1788a, 1788 b and 1788 c, and is electrically connected to one of thesesupport elements by a trace 1796 a.

In a further arrangement (FIG. 14), the support elements 1888 arearranged in rectilinear rows and columns, but the posts are disposed inthe rows or columns such that each post lies between two adjacentsupport elements 1888. Moreover, it is not essential to have aone-to-one association between posts, traces and support elements. Forexample, a given post may be connected by two or more traces to two ormore posts. Conversely, a given support element may be electricallyconnected to two or more posts. In yet another variant, one or more ofthe posts may be electrically connected to support elements remote fromsuch posts. Also, the flexible substrate may include elements such asconductive planes which serve as ground planes or power distributionplanes.

The support elements need not be electrically conductive. For example,as shown in FIG. 15, a package 1980 includes a flexible supportsubstrate 1990 supported over the front surface 1984 of a chip 1982 bysupport elements 1988 which are formed from a dielectric material as,for example, small spheres of glass or polymer. The traces 1996 on theflexible substrate, and hence the posts 1998, are electrically connectedto the contacts 1983 of the chip by wire bonds. Here again, the posts1998 are offset from the support elements 1988 so that the bases of theposts can move upon flexure of the support element 1990. In theembodiment of FIG. 15, some of the contacts 1983 a on the chip aredisposed in one or more rows adjacent the center of the chip, whereasothers are disposed in rows adjacent the edges of the chip. In a furthervariant (not shown), the contacts of the chip are connected to thetraces 1998 by leads formed integrally with the traces. Leads 1902extend to center contacts 1983 a through a slot or hole in substrate1990. Alternatively, two separate substrates can be positioned onopposite sides of the center contact row.

In yet another variant (FIG. 16) the flexible substrate 2090 issupported over a rear surface 2085, opposite from the contact-bearing orfront surface 2084. Stated another way, the chip is “face-up” relativeto substrate 2090. The traces 2096 of and hence the posts 2098 areelectrically connected to the contacts 2083 by leads 2002 such as wirebonds or leads integral with the traces. Here again, the posts 2098 areoffset from the support elements 2088 so that in this embodiment aswell, movement of the posts is facilitated by flexing of the substratebetween support elements. In the embodiment of FIG. 16, support elements2088 are nonconductive and are formed as portions of a continuous layer2004. Merely by way of example, such a continuous layer with projectingsupport elements may be formed by molding or embossing a polymericlayer.

The foregoing discussion has referred to an individual microelectronicelement. However, the package may include more than one microelectronicelement or more than one substrate. Moreover, the process steps used toassemble the flexible substrate, support elements and posts to chips maybe performed while the chips are in the form of a wafer. A single largesubstrate may be assembled to an entire wafer, or to some portion of thewafer. The assembly may be severed so as to form individual units, eachincluding one or more of the chips and the associated portion of thesubstrate. The testing operations discussed above may be performed priorto the severing step. The ability of the packages to compensate fornon-planarity in a test board or in the wafer itself greatly facilitatestesting of a large unit.

The posts may be fabricated separately from the substrate and traces andthen assembled to the substrate. One such a process uses a substrate2100 (FIG. 17) having a top dielectric layer 2102, a bottom dielectriclayer 2104 (FIG. 18) and traces 2106 extending between these dielectriclayers. Layer 2102 defines a top surface 2108 whereas bottom layer 2106defines a bottom surface 2110 of the substrate. Traces 2106 includeelongated sections 2112 and lands 2114 broader than elongated sections2112. The traces have holes 2116 disposed in the lands. The dielectriclayers 2102 and 2104 may or may not have holes aligned with holes 2116.Posts 2118 having elongated sections 2120 are forced through thesubstrate in the upward direction, from the bottom surface to the topsurface, as indicated by arrow F in FIG. 18. The posts embed themselvesin the substrate and are held in place by the elasticity of thesubstrate and the traces. The posts also make electrical contact withtraces 2106. Elongated portions 2120 of the posts protrude from the topsurface 2108.

The substrate and traces may deform locally in regions surrounding theposts. These regions tend to deform upwardly, leaving concavities 2124in the bottom surface of the substrate. The posts may have heads 2122,and these heads may be lodged partially or completely within theconcavities. To control deformation of the substrate, the top surface2108 of the substrate may be abutted against a die 2126 having holesaligned with locations where posts are forced through the substrate.Such a die can also help to prevent delamination of the substrate andtraces. In variants of the process, the traces may be disposed on thetop or bottom surface of a single-layer substrate. The resultingpost-array substrate can be assembled with a microelectronic element toform a package as discussed above, or can be used in any othermicroelectronic assembly where a small post array is desirable. Theassembly process allows selective placement of posts. It is notessential to provide the lands 2114 and holes 2116 in the traces. Thus,posts can be placed at any location along any trace. Moreover, the postsmay be formed from essentially any conductive material. Different postsmay be formed from different materials. For example, posts subject tosevere mechanical loading can be formed entirely or partially from hardrefractory metals such as tungsten, while other posts may be formed fromsofter metals such as copper. Also, some or all of the posts may beformed entirely or partially from corrosion-resistant metals such asnickel, gold or platinum.

As mentioned above, posts 2118 may include heads 2124 of larger diameterthan the other portions of the posts. As shown in FIG. 19, a post mayinclude features such as a knurl 2130 in the region of the post which isto engage the trace; a tapered configuration 2132. Alternatively oradditionally, a posts may include a narrow section 2134 having diametersmaller than the projecting section 2120 and a head 2136 having largerdiameter than narrow section 2134. This provides a snap action duringassembly; the substrate and trace stretch as section 2120 passes throughthem, and then snap back to engage the narrow section. In yet anotheralternative, the posts may have outwardly projecting barbs 2138 andheads 2140, so that the substrate and trace become engaged between thebarbs and the heads. The individual posts may be formed bymass-production processes of the type commonly used to make miniaturerod-like elements, such as cold-heading, thread rolling or precisionmachining.

In certain preferred embodiments of the present invention, a particlecoating such as that disclosed in U.S. Pat. Nos. 4,804,132 and5,083,697, the disclosures of which are incorporated by referenceherein, may be provided on one or more electrically conductive parts ofa microelectronic package for enhancing the formation of electricalinterconnections between microelectronic elements and for facilitatingtesting of microelectronic packages. The particle coating is preferablyprovided over conductive parts such as conductive terminals or the tipends of conductive posts. In one particularly preferred embodiment, theparticle coating is a metalized diamond crystal coating that isselectively electroplated onto the conductive parts of a microelectronicelement using standard photoresist techniques. In operation, aconductive part with the diamond crystal coating may be pressed onto anopposing contact pad for piercing the oxidation layer present at theouter surface of the contact pad. The diamond crystal coatingfacilitates the formation of reliable electrical interconnectionsthrough penetration of oxide layers, in addition to traditional wipingaction.

Referring to FIGS. 22A-22D, in accordance with certain preferredembodiments of the present invention, a connection component orinterposer 2380 includes a flexible, dielectric substrate 2390 having atop surface 2392 and a bottom surface 2394. The connection component2380 includes a plurality of conductive posts 2398 that are attached tothe flexible substrate 2390 and that project from the second surface2394 of the substrate. Each post 2398 preferably has a tip end 2376adapted for forming an electrical interconnection with a conductiveelement such as a contact pad. The connection component 2380 alsoincludes conductive traces 2396 having first ends 2400 and second ends2402 connected with the conductive posts 2398. The conductive traces2396 extend over the first surface 2392 of the flexible substrate 2390.

Before assembling the connection component 2380 with a microelectronicelement such as a semiconductor chip, the connection component 2380 ispositioned atop a sacrificial layer 2491 having openings 2493 extendingtherethrough. The openings 2493 may be formed by a laser, or by usingtechniques such as punching, drilling or etching. The sacrificial layer2491 has a top surface 2494, a bottom surface 2496 and a height H₁defined by the distance between the top surface and the bottom surface.The height H₁ is desirably greater than the height of the conductiveposts 2398. The sacrificial layer 2491 is preferably made of a heatresistant material.

The sacrificial layer 2491 may be attached to the connection component2380 either during or after fabrication of the connection component2380. An adhesive material 2498, such as an adhesive layer havingrelatively low tackiness, may be provided over the top surface 2494 ofthe sacrificial layer 2491. The adhesive material preferably temporarilyattaches the connection component 2380 to the sacrificial layer duringfabrication of the microelectronic assembly.

Referring to FIG. 22B, a microelectronic element 2382, such as asemiconductor chip, has contacts 2383 accessible at a front face 2384thereof. In order to assemble the microelectronic element 2382 with theconnection component 2380, the front face 2384 of the microelectronicelement is juxtaposed with the first surface 2392 of the flexiblesubstrate 2390.

Referring to FIG. 22C, conductive support elements 2388 are provided incontact with traces 2396 for electrically interconnecting themicroelectronic element 2382 with the connection component 2380. A layerof a compliant encapsulant 2327 may be disposed around the conductivesupport elements 2388 and between the microelectronic element 2382 andthe flexible substrate 2390.

Referring to FIG. 22D, an overmold 2495 is formed around themicroelectronic assembly. The overmold 2495 preferably covers the rearface and edges of the chip 2382 and the top surface 2392 of the flexiblesubstrate 2390. The overmold 2495 preferably prevents contamination ofthe assembly and adds stability to the package. Although the presentinvention is not limited by any particular theory of operation, it isbelieved that the sacrificial layer supports the flexible substrate 2390during assembly of the microelectronic assembly, and particularly whenforming the electrical interconnection between the microelectronicelement 2382 and the connection component 2380. The sacrificial layer2491 also preferably provides planarity for the components, such as whenthe overmold material flows under the microelectronic element 2382, soas to provide a thinner assembly. After the assembly has been completed,the sacrificial layer 2491 may be removed or stripped away to expose theconductive posts for connection with another microelectronic element.

FIG. 23 shows a microelectronic assembly atop a sacrificial layer 2591.The Sacrificial layer has a top surface 2594, a bottom surface 2596 andan opening 2593 extending between the top and bottom surfaces. Thesacrificial layer 2591 supports a connection component including aflexible substrate 2390 and conductive posts 2498. The assembly includesa microelectronic element 2482 having a front face 2484 with contacts2483 and a rear surface 2485 remote therefrom. The assembly alsoincludes support elements 2487 that abut against the rear face 2485 ofthe microelectronic element 2482 for supporting the microelectronicelement above the flexible substrate 2390. In the particular embodimentshown in FIG. 23, the support elements 2487 are preferablynon-conductive. The microelectronic element 2482 is electricallyinterconnected with conductive traces using conductive wire 2594. Anovermold 2595 is preferably formed over the microelectronic element 2482and the top surface 2492 of the flexible substrate 2490. Afterfabrication of the assembly, the sacrificial layer 2591 may be removedfor exposing the conductive posts 2498 so that the assembly may beelectrically interconnected with another microelectronic element, suchas a printed circuit board. The methods described above with referenceto FIGS. 22A-22D and 23 may also be performed on a wafer scale. Thesacrificial layer may be removed either before the wafer is severed orafter the wafer is severed into one or more packages.

As discussed above, the motion of the posts may include a tiltingmotion. This tilting motion causes the tip of each post to wipe acrossthe contact pad as the tip is engaged with the contact pad. Thispromotes reliable electrical contact. As discussed in greater detail inthe co-pending, commonly assigned application Ser. No. 10/985,126 filedNov. 10, 2004, entitled “MICRO PIN GRID ARRAY WITH WIPING ACTION,” thedisclosure of which is incorporated by reference herein, the posts maybe provided with features which promote such wiping action and otherwisefacilitate engagement of the posts and contacts. As disclosed in greaterdetail in the co-pending, commonly assigned application Ser. No.10/985,119 filed Nov. 10, 2004, entitled “MICRO PIN GRID WITH PIN MOTIONISOLATION,” the disclosure of which is also incorporated by referenceherein, the flexible substrate may be provided with features to enhancethe ability of the posts to move independently of one another and whichenhance the tilting and wiping action.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. A microelectronic package comprising: a microelectronic elementhaving faces and contacts; a flexible substrate spaced from andoverlying a first face of said microelectronic element; a plurality ofconductive posts extending from said flexible substrate and projectingaway from the first face of said microelectronic element, at least someof said conductive posts being electrically interconnected with saidmicroelectronic element; and a plurality of support elements disposedbetween said microelectronic element and said substrate and supportingsaid flexible substrate over said microelectronic element, at least someof said conductive posts being offset from said support elements.
 2. Thepackage of claim 1 wherein said first face is a front face of saidmicroelectronic element and said contacts are accessible at said frontface.
 3. The package of claim 2 wherein at least some of said supportelements are electrically conductive, said conductive support elementselectrically interconnecting at least some of the contacts of saidmicroelectronic element with at least some of said conductive posts. 4.The package of claim 3 wherein said microelectronic element is operableto interchange signals at a frequency above about 300 MHz through atleast some of said conductive posts.
 5. The package of claim 4 whereinat least some of said posts are connected to at least some of saidcontacts by conductive support elements immediately adjacent to suchposts.
 6. The package as claimed in claim 3, further comprisingconductive traces provided on said flexible substrate, wherein saidconductive traces electrically interconnect at least some of saidconductive posts with at least some of said conductive support elements.7. The package as claimed in claim 3, wherein said flexible substratehas a bottom surface facing the front face of said microelectronicelement and said conductive traces extend along the bottom surface ofsaid flexible substrate.
 8. The package as claimed in claim 3, whereinflexible substrate has a top surface facing away from the front face ofsaid microelectronic element and said conductive traces extend along thetop surface of said flexible substrate.
 9. The package as claimed inclaim 3, wherein said contacts are spaced from one another in a gridarray over the front face of said microelectronic element.
 10. Thepackage as claimed in claim 3, wherein at least one of said conductivesupport elements comprises a mass of a fusible material.
 11. The packageas claimed in claim 3, wherein at least one of said conductive elementscomprises a dielectric core and an electrically conductive outer coatingover the dielectric core.
 12. The package as claimed in claim 2, whereinsaid contacts are disposed in one or more rows extending along the frontface of said microelectronic element.
 13. The package as claimed inclaim 1, wherein said flexible substrate comprises a dielectric sheet.14. The package as claimed in claim 1, further comprising a compliantmaterial disposed between said flexible substrate and saidmicroelectronic element.
 15. The package as claimed in claim 1, whereinat least one of said conductive posts is elongated.
 16. The package ofclaim 1 wherein said support elements are disposed in an array so thatsaid support elements define a plurality of zones of said flexiblesubstrate, each such zone being bounded by a plurality of said supportelements defining corners of such zone, different ones of said postsbeing disposed in different ones of said zones.
 17. The microelectronicpackage of claim 16 wherein only one of said posts is disposed in eachof said zones.
 18. A microelectronic assembly comprising a package asclaimed in claim 1 and a circuit panel having contact pads, said postshaving tips remote from said flexible substrate confronting said contactpads and electrically connected thereto.
 19. The assembly as claimed inclaim 18 further comprising an electrically conductive bonding materialsecuring said posts to said contact pads.
 20. A microelectronic packagecomprising: a microelectronic element having a front face with contacts;a flexible substrate spaced from and overlying said microelectronicelement, said flexible substrate having a top surface facing away fromthe said microelectronic element and a bottom surface facing saidmicroelectronic element, said flexible substrate being supported abovesaid front face of said microelectronic element so that said substrateis at least partially unconstrained in flexure; a plurality ofconductive posts extending from said flexible substrate and projectingaway from said microelectronic element, wherein said conductive postshave a base facing toward said flexible substrate, said conductive postsbeing electrically connected to said microelectronic element; andfocusing elements mechanically interconnecting the bases of at leastsome of said conductive posts and said substrate, wherein said focusingelements have smaller areas than the bases of said conductive posts. 21.The microelectronic package as claimed in claim 20 further comprising aplurality of support elements disposed between said flexible substrateand said microelectronic element, said support elements supporting saidflexible substrate, at least some of said posts being offset from saidsupport elements.
 22. The microelectronic package as claimed in claim 21wherein at least some of said support elements are electricallyconductive, at least some of said posts being electrically connected tosaid microelectronic element through said support elements.
 23. Themicroelectronic package as claimed in claim 20 further comprisingelectrically conductive traces on said flexible substrate, at least someof said focusing elements being electrically conductive and electricallyinterconnecting at least some of said posts to at least some of saidtraces.
 24. A method of processing a microelectronic package comprisingthe step of advancing a microelectronic package having a flexiblesubstrate supported over a surface of a microelectronic element andhaving electrically conductive posts projecting from said substrateuntil tips of said posts engage contact pads and said substrate flexesso that at least some base portions of said posts adjacent saidsubstrate move relative to the microelectronic element.
 25. The methodas claimed in claim 24 wherein said package includes support elementsdisposed between said microelectronic element and said flexiblesubstrate, said posts being at least partially offset from said supportelements, said offset facilitating said flexing.
 26. A method as claimedin claim 24 further comprising maintaining said tips in contact withsaid contact pads and testing said package during said maintaining step.27. A method as claimed in claim 26 further comprising disengaging saidtips from said contact pads after said testing step.
 28. A method asclaimed in claim 27 further comprising bonding said pads to electricallyconductive elements of a circuit panel after said disengaging step. 29.A method as claimed in claim 24 wherein said contact pads aresubstantially planar and said advancing step is conducted so as to movethe package with a component of motion orthogonal to the planes of saidpads.
 30. A microelectronic assembly comprising: (a) a microelectronicpackage having an exposed surface and a plurality of metallic postsprojecting from said exposed surface, said posts having tips remote fromsaid exposed surface; (b) a circuit panel having contact pads, said tipsof said posts confronting said contact pads; (c) a bonding materialsecuring said tips of said posts to said contact pads, said bondingmaterial extending between said tips and said pads and forming filletsextending around said tips of said posts.
 31. The assembly of claim 30wherein said tips of said posts have diameters that are smaller thansaid contact pads.
 32. The assembly of claim 30 wherein said packageincludes a microelectronic element and a flexible substrate at leastpartially unconstrained in flexure, said posts being mounted to saidflexible substrate so that said posts can move relative to saidmicroelectronic element upon flexure of said substrate.
 33. Amicroelectronic assembly comprising: (a) a microelectronic packagehaving an exposed surface and a plurality of metallic posts projectingfrom said exposed surface, said posts having tips remote from saidexposed surface; (b) a circuit panel having contact pads, said tips ofsaid posts confronting said contact pads; (c) a bonding materialsecuring said tips of said posts to said contact pads, said bondingmaterial extending between said tips and said pads; and (d) an underfilllayer at least partially surrounding at least some of said tips and atleast some of said pads, said underfill layer being spaced apart fromsaid exposed surface of said package.
 34. A method of making a postarray substrate comprising the steps of: (a) providing a flexiblesubstrate having traces thereon, said substrate having top and bottomsurfaces and; (b) forcing a plurality of posts through said substratefrom said bottom surface so that said posts penetrate at least some ofthe traces and make electrical contact therewith, and so that said postsproject from said top surface.
 35. The method of claim 34 wherein saidtraces have elongated sections and lands broader than said elongatedsections, and wherein said forcing step is performed so that said postspenetrate said lands.
 36. The method of claim 34 wherein, prior to saidforcing step, said traces have holes therein, and wherein said forcingstep is performed so that said posts pass through said holes.
 37. Themethod of claim 34 wherein said forcing step is performed so that saidsubstrate and portions of said traces are deformed upwardly in regionssurrounding each post.
 38. The method of claim 37 wherein saidupwardly-deformed regions define concavities in said bottom surface, andwherein said forcing step is performed so as to place heads on saidposts at least partially within said concavities.
 39. The method ofclaim 34 further comprising assembling said substrate with amicroelectronic element after said forcing step so that said top surfaceof said substrate faces away from the microelectronic element.
 40. Themethod as claimed in claim 39 wherein said assembling step includessupporting said substrate above said microelectronic element so thatsaid substrate is at least partially free to flex.
 41. A method ofmaking a microelectronic assembly comprising: providing a sacrificiallayer having a top surface, a bottom surface and openings extendingbetween the top and bottom surfaces, said sacrificial layer having aheight between the top and bottom surfaces thereof; juxtaposing aflexible dielectric substrate with the top surface of said sacrificiallayer, said flexible substrate having a plurality of conductive postsprojecting from a bottom surface thereof, said conductive posts havingtip ends defining a second height from the bottom surface of saidsubstrate; inserting said conductive posts into said openings of saidsacrificial layer and abutting the bottom surface of said flexiblesubstrate against the top surface of said sacrificial layer, wherein theheight of said conductive posts is less than the height of saidsacrificial layer.
 42. The method as claimed in claim 41, furthercomprising: connecting a microelectronic element with said flexiblesubstrate; and electrically interconnecting said microelectronic elementwith said conductive posts.
 43. The method as claimed in claim 42,further comprising: providing an overmold over said electricallyinterconnected microelectronic element; and after the providing anovermold step, detaching said sacrificial layer from said flexiblesubstrate.
 44. The method as claimed in claim 41, further comprisingproviding an adhesive between said substrate and said sacrificial layerbefore the abutting step.
 45. The method as claimed in claim 44, whereinthe providing an adhesive includes providing the adhesive over the topsurface of said sacrificial layer before the abutting step.
 46. Themethod as claimed in claim 42, further comprising providing conductivetraces over the top surface of said flexible substrate, and electricallyinterconnecting said conductive traces with said conductive posts. 47.The method as claimed in claim 46, wherein said microelectronic elementhas a first face including contacts, and wherein the first face of saidmicroelectronic element confronts the top surface of said flexiblesubstrate.
 48. The method as claimed in claim 46, wherein saidmicroelectronic element has a first face including contacts, and whereinthe first face of said microelectronic element faces away from the topsurface of said flexible substrate.
 49. The method as claimed in claim42, wherein the electrically interconnecting step includes using one ormore wire bonds for connecting contacts of said microelectronic elementwith the traces on said flexible substrate.
 50. The method as claimed inclaim 42, wherein the electrically interconnecting step includes using aconductive mass for connecting contacts of said microelectronic elementwith the traces of said flexible substrate.